Booting a Custom Kernel in QEMU using UEFI
In this article, we will discuss the process of booting a custom kernel in QEMU using UEFI. This is a common task for those developing their own operating system or experimenting with low-level systems programming.
Prerequisites
Before we begin, make sure you have the following tools installed:
- QEMU
- UEFI firmware (e.g. OVMF)
- A custom kernel (e.g. a simple "Hello World" kernel)
Setting up the UEFI Firmware
First, we need to set up the UEFI firmware in QEMU. This can be done using the following command:
$ qemu-system-x86\_64 -bios -M q35 -m 1024
This will start QEMU with the specified UEFI firmware and a Q35 machine type with 1024MB of memory.
Creating a UEFI Shell Application
Next, we need to create a UEFI shell application that will load our custom kernel. This can be done using the UEFI Shell Application (USAF) format. Here is an example of a simple UEFI shell application that loads a kernel:
#include <Uefi.h>
EFI\_STATUS
EfiMain (
IN EFI\_HANDLE ImageHandle,
IN EFI\_SYSTEM\_TABLE \*SystemTable
) {
EFI\_LOADED\_IMAGE \*LoadedImage;
EFI\_STATUS Status;
Status = gBS->OpenProtocol (
ImageHandle,
&LoadedImage->Protocol,
(VOID **)&LoadedImage,
ImageHandle,
NULL,
EFI\_OPEN\_PROTOCOL\_BY\_HANDLE\_PROTOCOL
);
if (EFI\_ERROR (Status)) {
return Status;
}
Status = gBS->LoadImage (
False,
ImageHandle,
LoadedImage->DeviceHandle,
LoadedImage->FilePath,
0,
&LoadedImage->Image,
NULL,
&LoadedImage->ImageSize
);
if (EFI\_ERROR (Status)) {
return Status;
}
Status = gBS->StartImage (
LoadedImage->Image,
LoadedImage->ImageSize,
0,
NULL);
return Status;
}
This application simply loads the specified image and starts it. Note that the image must be in the same directory as the UEFI shell application.
Booting the Custom Kernel
Finally, we can boot our custom kernel using the following command:
$ qemu-system-x86\_64 -bios -M q35 -m 1024 -drive if=pflash,format=raw,readonly,file= -drive if=none,file=,id=hd -device ide-drive,drive=hd
This will start QEMU with the specified UEFI firmware, load the UEFI shell application, and then boot the custom kernel. If everything is set up correctly, you should see the output of your custom kernel in the QEMU window.
In this article, we have discussed the process of booting a custom kernel in QEMU using UEFI. We have covered the following key concepts:
- Setting up the UEFI firmware in QEMU
- Creating a UEFI shell application to load the custom kernel
- Booting the custom kernel in QEMU using the UEFI shell application